ALLOCATION OF SUB CHANNELS OF MlMO CHANNELS OF A WIRELESS NETWORK

ABSTRACT

A base station for wireless network uses one or more MIMO channels having subchannels, to communicate with multiple user equipments, and allocates the sub channels to the user equipments. Different subchannels of a given one of the channels can be allocated to different user equipments. The ability to allocate sub channels individually rather than only allocating entire channels can enable higher data rates can be achieved. This is particularly useful for improving data rates at cell boundaries or sector boundaries, where the coverage is traditionally weakest. A user equipment can use subchannels from different MIMO channels from different sectors or from different base stations.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Ser. No. 10/360,486, filedFeb. 6, 2003, which is hereby incorporated by reference.

FIELD OF THE INVENTION

This invention relates to base stations for wireless networks, to userequipments for wireless networks, to methods of allocating sub channelsand to methods of offering a data transmission over such networks.

BACKGROUND TO THE INVENTION

A MIMO (Multiple Input, multiple output) wireless communication system(see FIG. 1) is one which comprises a plurality of antennas at thetransmitter and one or more antennas at the receiver. The antennas areemployed in a multi-path rich environment such that due to the presenceof various scattering objects (buildings, cars, hills, etc.) in theenvironment, each signal experiences multipath propagation. Thus thereare numerous scattered signals between the transmit and receiveantennas. User data is transmitted from the transmit antennas using aMIMO transmission method, for example space-time coding (STC) or BLASTas is known in the art, typically with many channels separated byfrequency, time slots, or coding. The receive antennas capture thetransmitted signals and a signal processing technique is then applied asknown in the art, to separate the transmitted signals and recover theuser data. FIG. 1 shows a base station BS1 having two or more spatiallyseparated antennas, transmitting to corresponding antennas on userequipment UE1. It is not untypical for one of the MIMO channels to havemuch better reception than the other, despite the close proximity of therespective antennas.

MIMO wireless communication systems are advantageous in that they enablethe capacity of the wireless link between the transmitter and receiverto be improved compared with previous systems in the respect that higherdata rates can be obtained. The multipath rich environment enablesmultiple channels (these are what are referred to as sub-channels in theremainder of the document) to be transmitted between the transmitter andreceiver, and distinguished at the receiver only by the spatialcharacteristics, even though the same frequency, code or time slot isused. Even line of sight signals can potentially be separated into MIMOsub channels based on spatial characteristics. Data for a single usercan then be transmitted over several paths in the air by inversemultiplexing the data into several streams. These are transmittedsimultaneously using the same frequency or time slots or codes, andremultiplexed at the receiver. Consequently, higher spectralefficiencies are achieved than with non-MIMO systems.

Also, as the multipath characteristic varies with time, especially formobile users, adaptive modulation coding (AMC) can be used to achievehigher data rates where the multipath and interference and noise allow.Conventional hand off techniques are used in cell based MIMO systems tohand off all streams of a MIMO channel to a neighboring base station.The trigger for such a “hard” hand off is usually a signal strengthindication of the downlink, measured at the user equipment.

US Patent Application 20030003863 shows link adaptation for MIMOtransmission schemes. Information to be transmitted is divided into aplurality of subsignals (defined as the signal carried on a subchannel).In the receiver the different receive signals are processed so thatsubsignals are detected and decoded and the contribution of eachdetected and decoded subsignal is subtracted from the receive signals. Afeedback channel from receiver to transmitter is used to send controlinformation to the transmitter to optimize the usage of the MIMOchannel. In the receiver, the link quality of each subsignal isdetermined and is transmitted to the receiver via the feedback channel.In the transmitter, the link quality information can be used to vary thedata rate of each subsignal, vary the transmit power of each subsignal,vary the modulation scheme of each subsignal, vary the coding scheme ofeach subsignal or vary any combination of these properties. Furthermore,the link quality determination may be based on an error ratemeasurement, a noise ratio measurement, or a capacity measurement Thelink quality measurement may be fast-adaptive, e.g. when it is based onthe instantaneous calculated capacities of each subsignal. Fast meansthat the measurement period is shorter or substantially equal to thetime period in which fast fading becomes relevant. As fast fading isdependant on the Doppler shift of the signal, the time period is alsodependent on the velocity a receiver moves relative to the transmitter.For slow-adaptive embodiments a capacity calculation based on an averageof the calculated capacities of each layer with respect to a longer timeperiod or a capacity calculation that takes the outage of the calculatedcapacities of each layer with respect to a longer time period, may beapplied.

One limitation with existing MIMO systems concerns the large size of thetransmit and receive antenna arrays. Another limitation with existingMIMO systems is that they are designed for use in environments wherescattering occurs rather than for line of sight situations. Moresignificant in many cases are the following limitations:

-   -   a) The coverage of MIMO systems can be very uneven. MIMO        provides much improved data rates for users with good C/I,        typically near the base station, but provides little improvement        to users in a poor C/I situation (typically at cell edges) so        their data rate remains low.    -   b) The ‘sub-channels’ of a MIMO system often have very uneven        capacity. This is dependent on the propagation characteristics        of the channel and can be particularly uneven in a propagation        environment where one multipath component is very dominant.        These poor quality sub-channels are used to provide a very small        additional data rate to the user which is wasteful.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide improved apparatusand methods. According to a first aspect of the present invention, thereis provided a base station for a wireless network for communicating overone or more channels to multiple user equipments, at least one of thechannels having sub channels distinguishable by spatial separation oftransmitters of the respective sub channels, the base station having anallocator for allocating the sub channels to the user equipments, theallocator being arranged to allocate different subchannels of a givenone of the channels to different user equipments.

Notably, the ability to allocate sub channels individually, rather thanonly allocating entire channels can enable higher data rates to beachieved. It is based on a recognition that different sub channels cansupport widely differing data rates to a given user equipment, so itmight be more efficient to reallocate a sub channel having a lower datarate to a different user equipment for which it can achieve a higherdata rate. This is particularly useful for improving data rates at cellboundaries or sector boundaries, where the coverage is traditionallyweakest. The channels can be MIMO, for use with MIMO capable userequipment or MISO (Multiple input single Output) with appropriate signalprocessing at the receiver.

In principle, an alternative is to make the allocation at the userequipment. It is usually more convenient to make the allocation at thetransmitter side, which is the base station for the downlink. This ispreferred because the base station has information on the signal qualityand data rate requirements of all users so can allocate MIMO subchannelsbased an upon that more complete knowledge of the network. Theallocation for the uplink can follow the downlink allocation or beallocated independently. The latter is preferred if the fadingcharacteristics of the propagation channel has low correlation betweenthe uplink and downlink. If there is good correlation between uplink anddownlink fading, then using the downlink allocation will be a goodapproximation.

The base station can be of any type. It need not necessarily be at afixed location, and can be distributed or incorporated partly intomobile terminals in principle, without losing the advantages set outabove.

An additional feature of some embodiments is the base station beingarranged to cooperate with a neighboring base station to enablesubchannels from both base stations to be allocated to the same userequipment This is particularly useful for user equipment near theboundary of coverage from two base stations.

An additional feature of some embodiments is the allocator beingarranged to allocate the sub channels for downlinks according toinformation relating to sub channel signal quality received from theuser equipment. This can help ensure the allocation is made with thebest information available.

An additional feature of some embodiments is the information comprisingsignal quality measurements of sub channels allocated to the userequipment, and sub channels available but not allocated. This is the“raw” information useful for optimizing the allocation.

An additional feature of some embodiments is the information comprisinga request to allocate a different sub channel. This is intended to coverthe option of the “raw” information being processed in the userequipment so that less information need be passed to the base station.

An additional feature of some embodiments is different transmitters fordifferent sectors, the allocator being arranged to allocate sub channelsfrom more than one sector to the same user equipment. This isparticularly useful for user equipment located near the boundary ofsectors.

An additional feature of some embodiments is a signal quality detectorfor measuring signal quality of uplinks, the allocator using thesemeasurements to allocate sub channels for the uplink. Independentallocation of uplinks can improve overall efficiency.

An additional feature of some embodiments is the base station beingarranged to adapt modulation and/or coding of the sub channels. This canfurther help improve coverage at the highest data rates. The adaptationcan be on the basis of measurements of signal quality.

The invention also provides a user equipment for communicating with abase station of a wireless network over multiple channels, at least someof the channels having sub channels distinguishable by spatialseparation of transmitters of the respective sub channels, the userequipment having a signal quality detector for measuring the signalquality of sub channels, and being arranged to use subchannels selectedfrom more than one of the channels.

This is notable for enabling more efficient use of potential availablecapacity.

An additional feature of some embodiments is comparing sub channels fromdifferent base stations.

An additional feature of some embodiments is comparing sub channels fromdifferent sectors of a base station.

An additional feature of some embodiments is sending signal qualitymeasurements of the sub channels to the base station.

The invention also provides an allocator for the base station, in theform of software. This acknowledges that software can be a valuable,separately tradable commodity. It is intended to encompass software,which runs on or controls “dumb” or standard hardware, to carry out thedesired functions. For similar reasons, it is also intended to encompasssoftware which “describes” or defines the configuration of hardware,such as HDL (hardware description language) software, as is used fordesigning silicon chips, or for configuring universal programmablechips, to carry out desired functions.

The invention also provides a method of allocating sub channels in awireless network having multiple channels between a base station andmultiple user equipments, at least some of the channels having subchannels distinguishable by spatial separation of transmitters of therespective sub channels, the method having the steps of receiving anindication of signal qualities of the sub channels, and allocating thedifferent subchannels of a given one of the channels to different userequipments according to the signal qualities.

The invention also provides a method of offering a data transmissionservice over a wireless network using the base station. The advantagesof the invention can enable improvements to be made in the system ornetwork performance such as being more reliable (better coverage ofhigher data rates for example) or more flexible, having a greatercapacity, or being more cost effective. Consequently data transmissionservices over the network can be enhanced, and the value of suchservices can increase Such increased value of services over the life ofthe system, could prove far greater than the sales value of theequipment.

Another aspect of the invention provides a base station for a wirelessnetwork for communicating over one or more channels to multiple userequipments, at least one of the channels having sub channelsdistinguishable by spatial separation of transmitters of the respectivesub channels, the base station having an allocator for allocating morethan one of the channels to a given one of the user equipments. This caninclude all the subchannels, or involve selecting the best subchannelsfrom each channel.

An additional feature of some embodiments is the base station beingarranged to cooperate with other base stations to allocate channels frommore than one base station to the given user equipment.

The invention also provides user equipment for communicating with a basestation of a wireless network over multiple channels, at least some ofthe channels having sub channels distinguishable by spatial separationof transmitters of the respective sub channels, the user equipmenthaving a signal quality detector for measuring the signal quality of subchannels, and being arranged to use more than one of the channelssimultaneously.

Any of the features can be combined with any of the aspects of theinvention as would be apparent to those skilled in the art. Otheradvantages will be apparent to those skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

To show by way of example how the invention can be implemented,embodiments will now be described with reference to the figures inwhich:

FIG. 1 shows a base station and user equipment of a prior ad MIMOarrangement,

FIGS. 2 and 3 show schematic views of embodiments of the invention usingtwo base stations and user equipment'

FIG. 4 shows a sequence chart of the arrangement of FIG. 2,

FIG. 5 shows a schematic view of an embodiment using multiple MIMOchannels from a single base station, and

FIG. 6 shows a sequence chart of the arrangement of FIG. 5.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS FIGS. 2 and 3, EmbodimentUsing Two Base Stations

FIG. 2 shows base station BS1 in cell 1 and base station BS2 in cell 2.User equipment UE1 is initially served by a MIMO channel from BS1 havingsubchannels 1 and 2. As UE1 moves towards 8S2 it is additionally servedby a MIMO channel from BS2, without dropping the MIMO channel from BS1.This means that data rate coverage in call border regions can beimproved, since UE1 has four subchannels to receive data. To achievethis, the traffic for UE1 needs to be split by an RNC (radio networkcontroller) between BS1 and BS2. This can be implemented by signallingover management channels to advise the RNC which base stations can serveUE1, following conventional practice.

FIG. 3 shows another embodiment using two base stations. Similarelements are shown to those in FIG. 2 and corresponding reference signsare used where appropriate. In FIG. 3 two user equipments UE1 and UE2are in a cell border region. UE1 is initially served by a MIMO channelfrom BS1. UE2 is initially served by a MIMO channel from BS2. Both MIMOchannels have two subchannels For each MIMO channel one of thesubchannels is stronger than the other, If UE1 detects a stronger signalfrom BS2 than the poorer of its subchannels from BS1, it will requestthat it receives that stronger subchannel from BS2. Likewise if UE2detects a stronger signal from BS1 it will request that it receives thatstronger subchannel from BS1. As shown in the figure, UE1 will drop itspoorer subchannel from BS1 and add a stronger subchannel from B52. UE1will ignore the poorer subchannel from BS2. Likewise UE2 will add thestronger subchannel from BS1, ignore the poorer subchannel from BS1 anddrop its poorer from BS2. The respective subchannels which are droppedare taken up by the other user equipment which can achieve a higher datarate since there is better reception. Hence this swapping of subchannelscan improve the data rate for both user equipments, and overall networkcapacity is improved in the cell border areas which are conventionallythe areas of worst coverage.

FIG. 4, Sequence Chart for FIG. 2

This chart shows some of the principal actions of each of the entities.As a preliminary step BS1 and BS2 periodically report to the RNC whichbase stations are nearest to a given UE. The RNC then sends all thetraffic for a given UE to several “best” base stations. UE1 regularlymeasures pilot signal quality. Pilot signals are sent out by all basestations. If UE1 finds that the signal from BS2 is stronger than anyother the subchannels it is currently using from BS1, it will report themeasurements or request a change of allocation. The base stations willdetermine a new allocation according to the measurements for therequests. The new allocation information will be sent to UE1 over amanagement channel then transmissions can start to UE1 from both basestations.

FIG. 5, Embodiment Using Multiple MIMO Channels from a Single BaseStation

FIG. 5 shows an embodiment in which there are multiple MIMO channelsfrom a single base station. These channels can correspond to differentsectors of the base station, or the same sector. User equipments UE1 andUE2 are served by base station BS1, Conventionally and initially UE1 isserved on MIMO Channel 1 (subchannels 1 and 2) and UE2 is served onChannel 2 (subchannels 1 and 2). If as shown subchannel 2 of channel 1becomes poor in terms of signal quality, it can be dropped. Ifsubchannel 1 of channel 2 becomes poor it can be dropped. If the signalquality of these poor channels is better at another UE, then areallocation of sub channels can take place. As shown, UE1 is now servedon channel 1 subchannel 1 and channel 2 sub-channel 1. UE2 is now servedon channel 1 subchannel 2 and channel 2 sub-channel 2. Coverage can beimproved (Mend UE2 have improved their data rate), In addition thenetwork capacity can be improved. This represents a way of optimisingfor network capacity while also improving coverage shown operating in asingle cell.

FIG. 6, sequence chart for the embodiment of FIG. 5

FIG. 6 shows a sequence chart for the embodiment of FIG. 5. As before,the user equipment measures pilot signal quality. UE1 and UE2 sendmeasurement information or request service on the best sub channels. BS1then allocates the subchannels according to the measurements oraccording to the requests. The allocation information is sent to UE1 andUE2 over a management channel. Then transmission of the traffic canbegin.

CONCLUDING REMARKS

As has been described above, a base station for a wireless network usesone or more MIMO) channels having subchannels, to communicate withmultiple user equipments, and allocates the sub channels to the userequipments. Different subchannels of a given one of the channels can beallocated to different user equipments. The ability to allocate subchannels individually, rather than only allocating entire channels canenable higher data rates can be achieved. This is particularly usefulfor improving data rates at cell boundaries or sector boundaries, wherethe coverage is traditionally weakest. A user equipment can usesubchannels from different MIMO channels from different sectors or fromdifferent base stations. Other variations will be apparent to thoseskilled in the art, having corresponding advantages to those set outabove, within the scope of the claims.

1. A method of allocating subchannels in a wireless network havingmultiple channels between a base station and multiple user equipments,at least some of the channels having subchannels distinguishable byspatial separation of the subchannels, the method comprising: receivingindications of signal qualities of subchannels from a first userequipment and a second user equipment; and allocating a first subchannelof a first channel to the first user equipment and a second subchannelof the first channel to the second user equipment, the first subchanneland the second subchannel of the first channel being distinguishable byspatial separation.
 2. A method as defined in claim 1, wherein thesecond subchannel of the first channel is allocated to the second userequipment instead of the first user equipment only when the signalquality of the second subchannel of the first channel is better at thesecond user equipment than at the first user equipment.
 3. A method asdefined in claim 1, further comprising: initially allocating the firstsubchannel of the first channel and the second subchannel of the secondchannel to the first user equipment; receiving the indications of signalqualities of the first and second subchannels of the first channel fromthe first and second user equipments; and reallocating the secondsubchannel of the first channel to the second user equipment when thereceived signal quality indications indicate that the signal quality ofthe second subchannel of the first subchannel is higher at the seconduser equipment than at the first user equipment.
 4. A method as definedin claim 1, wherein the first subchannel of the first channel isallocated to the first user equipment at a first base station, themethod further comprising allocating the first subchannel of the firstchannel to the first user equipment at a second base station forsimultaneous communication between the first base station and the firstuser equipment and between the second base station and the first userequipment.
 5. A base station for a wireless network having multiplechannels between a base station and multiple user equipments, at leastsome of the channels having subchannels distinguishable by spatialseparation of the respective subchannels, the base station comprising: areceiver operable to receive indications of signal qualities ofsubchannels from a first user equipment and a second user equipment; anda processor operable to allocate a first subchannel of a first channelto the first user equipment and a second subchannel of the first channelto the second user equipment, the first subchannel and the secondsubchannel of the first channel being distinguishable by spatialseparation.
 6. A base station as defined in claim 5, wherein theprocessor operable to allocate the second subchannel of the firstchannel to the second user equipment instead of the first user equipmentonly when the signal quality of the second subchannel of the firstchannel is better at the second user equipment than at the first userequipment.
 7. A base station as defined in claim 5, wherein theprocessor is operable: to allocate the first subchannel of the firstchannel and the second subchannel of the second channel to the firstuser equipment initially; and to reallocate the second subchannel of thefirst channel to the second user equipment when the received signalquality indications indicate that the signal quality of the secondsubchannel of the first subchannel is higher at the second userequipment than at the first user equipment.
 8. A base station as definedin claim 5, further comprising a transmitter operable to transmit pilotsignals on spatially separated subchannels to the first user equipmentand the second user equipment to enable the first user equipment and thesecond user equipment to determine signal qualities of the first andsecond subchannels of the first channel.
 9. A wireless networkcomprising: a radio network controller; and at least one base stationoperable to communicate over channels with first and second userequipments and to receive indications of signal qualities of subchannelsfrom a first user equipment and a second user equipment; wherein theradio network controller and the base station are co-operable toallocate a first subchannel of a first channel to the first userequipment and a second subchannel of the first channel to the seconduser equipment, the first subchannel and the second subchannel of thefirst channel being distinguishable by spatial separation.
 10. Awireless network as defined in claim 9, wherein the radio networkcontroller and the base station are co-operable to allocate the secondsubchannel of the first channel to the second user equipment instead ofthe first user equipment only when the signal quality of the secondsubchannel of the first channel is better at the second user equipmentthan at the first user equipment.
 11. A wireless network as defined inclaim 9, wherein the wireless network controller and the base stationare co-operable: to allocate the first subchannel of the first channeland the second subchannel of the second channel to the first userequipment initially; and to reallocate the second subchannel of thefirst channel to the second user equipment when the received signalquality indications indicate that the signal quality of the secondsubchannel of the first subchannel is higher at the second userequipment than at the first user equipment.
 12. A wireless network asdefined in claim 9, comprising first and second base stations operableto communicate with the first and second user equipments and to receiveindications of signal qualities of subchannels from the first userequipment and the second user equipment, wherein: the radio networkcontroller and the first base station are co-operable to allocate thefirst subchannel of the first channel to the first user equipment forcommunication between the first base station and the first userequipment; and the radio network controller and the second base stationare co-operable to allocate the first subchannel of the first channel tothe first user equipment at a second base station for communicationbetween the second base station and the first user equipmentsimultaneous with the communication between the first base station andthe first user equipment.
 13. A network entity for a wireless networkhaving multiple OFDM channels between a base station and multiple userequipments, at least some of the channels having subchannelsdistinguishable by spatial separation of the respective subchannels, thenetwork entity comprising: network entity hardware; and network entitysoftware executable on the network entity hardware to allocate a firstsubchannel of a first OFDM channel to the first user equipment and asecond subchannel of the first OFDM channel to the second user equipmentbased on indications of signal quality at the first and second userequipments of the first and second subchannels of the first OFDMchannel, the first subchannel and the second subchannel of the firstOFDM channel being distinguishable by spatial separation.
 14. A networkentity as defined in claim 13, wherein the network entity software isexecutable to allocate the second subchannel of the first OFDM channelto the second user equipment instead of the first user equipment onlywhen the signal quality of the second subchannel of the first OFDMchannel is better at the second user equipment than at the first userequipment.
 15. A network entity as defined in claim 13, wherein thesoftware is executable: to allocate the first subchannel of the firstOFDM channel and the second subchannel of the second OFDM channel to thefirst user equipment initially; and to reallocate the second subchannelof the first OFDM channel to the second user equipment when the receivedsignal quality indications indicate that the signal quality of thesecond subchannel of the first OFDM subchannel is higher at the seconduser equipment than at the first user equipment.
 16. A network entity asdefined in claim 13, wherein the network hardware comprises atransmitter operable to transmit at least one pilot signal fromspatially separated antennas to the first user equipment and the seconduser equipment to enable the first user equipment and the second userequipment to determine signal qualities of the first and secondsubchannels of the first OFDM channel.
 17. A user equipment forcommunicating over multiple subchannels of multiple channels, each ofthe channels having at least two subchannels distinguishable by spatialseparation of transmission at a base station, the user equipmentcomprising: a signal quality detector for measuring signal qualities ofsubchannels of channels, the subchannels of respective channels beingdistinguishable by spatial separation of transmission at the basestation; a communications component operable to simultaneously use asubchannel of a first channel and a subchannel of a second channel. 18.A user equipment as defined in claim 17, further comprising atransmitter operable to send signal quality indications for detectedsubchannels of channels to the base station.
 19. A user equipment asdefined in claim 17, wherein the channels comprise multiple inputmultiple output (MIMO) channels and the user equipment is operable touse more than one of the MIMO channels simultaneously.
 20. A userequipment as defined in claim 17, wherein the channels comprise multipleinput single output (MISO) channels and the user equipment is operableto use more than one of the MISO channels simultaneously.